This invention is directed to clutches, and more particularly to centrifugal clutches.
Centrifugal clutches are well known in the art. In essence, these devices, sometimes known as frictional contact axial clutches, utilize mating frictional members to transfer torque from an input shaft to an output shaft. This is accomplished by harnessing the effects of centrifugal force upon pivoted weights to generate axial movement and ultimately axial thrust. This axial thrust is applied upon an output frictional member which, by interacting with an input shaft frictional member, effectively transmits the input shaft torque to the output or driven shaft.
In one such type of clutch, weights are attached to a support disc which is mounted for rotation with a rotating input shaft. The weights are mounted to pivot about an axis perpendicular to the rotational axis of a support disc. The weights are spring biased to a non-engaging position relative to a clutch plate. As the angular speed increases, the weights pivot as the centrifugal force of the pivoting weights overcome the force generated by the springs and engage the clutch plate. With increasing angular speed, the weights pivot more and the clutch plate engages a clutch disc which is splined to an output drum. The plurality of springs which are operative between the support disc and the clutch plate pull the clutch plate toward the support disc. Thus, as the angular speed decreases, the springs push against the pivoted weights to restore the weights to their non-engaging, i.e., non-pivoted, position. Consequently, the clutch plate disengages the clutch disc such that the output drum is not actively driven.
There are several disadvantages associated with the type of clutch described above. One particular problem associated with this centrifugal clutch is frictional induced hysteresis. Friction acting upon the springs and weights causes the clutch to engage at one speed yet disengage at another speed. Typically, the frictional induced hysteresis causes the clutch to engage at a higher speed but disengage at a lower speed. Preferably, the engagement and disengagement speeds are substantially equivalent to one another, allowing for smoother operation of the centrifugal clutch when used on motorized vehicles such as racing karts. Additionally, adjusting the springs to achieve different engagement speeds is difficult, imprecise, and cumbersome.
What is needed, therefore, is a centrifugal clutch which is kinematically simpler so as to minimize frictional induced hysteresis during its operation to provide a centrifugal clutch with substantially equivalent engagement and disengagement speeds. This clutch should also be less complicated, less expensive, and relatively lightweight. Finally, the springs such be designed to be relatively simple to adjust and replace in order to allow for efficient adjustment of the engagement speed.
The present invention is directed to a kinematically simple centrifugal clutch which minimizes frictional induced hysteresis. The centrifugal clutch also provides an efficient and precise manner to adjust the clutch""s engagement speed. To that end and in accordance with the principles of the present invention, the centrifugal clutch includes a rotatable output driven member, at least one drive plate, and at least one clutch disc disposed adjacent to the drive plate. The clutch disc is mounted for rotation with the driven member. A drive hub is adapted to receive a rotational input such as that from an output shaft of a motor. The drive hub is mounted for rotation with the drive plate. At least one weighted member is pivotally mounted to the drive hub. The weighted member has at least two adjustment holes. At least one spring member is operative between the drive hub and the weighted member to bias the weighted member to a normally disengaged position relative to the drive plate. The spring member has one end selectively movable between the two adjustment holes. Various types of spring members, such as torsion springs or extension springs, could be utilized. Under the influence of centrifugal force generated by the rotation of the drive hub, the weighted member pivots against the resistance of the spring member so as to engage the drive plate and thereby urge the drive plate into engagement with the clutch disc to rotate the driven member in unison with the rotating drive hub. As the rotational speed of the drive hub decreases, the centrifugal force is overcome by the restoring force of the spring member and the weighted member pivots out of engagement with the drive plate, causing the drive plate to disengage the clutch disc. Consequently, the driven member is no longer actively driven by the clutch disc. The restoring force of the spring member can be adjusted by moving the end of the spring to a different adjustment hole in the weighted member.
In one embodiment, the drive hub also includes at least two adjustment holes associated with the spring. As such, the other end of the spring member is selectively movable between the adjustment holes in the drive hub. Consequently, the restoring force of the spring member can be adjusted by moving the respective ends of the spring between the adjustments holes in the weighted member and the drive hub.
In another embodiment, the centrifugal clutch includes at least two weighted members. Instead of each weighted member having at least to adjustment holes, each weighted member includes at least two adjustment slots. The centrifugal clutch further includes a garter spring that is coupled between one of the two adjustment slots of each of the weighted members to bias each weighted member to a disengaged position. The bias force exerted by the garter spring can be adjusted by moving the garter spring to a different adjustment slot in each of the weighted members.
Although the centrifugal clutch of the present invention may be used in applications requiring a clutch mechanism intermediate to a drive motor and a drive wheel, it is specifically adapted for application in motorized carts, especially racing karts.
The invention also contemplates a method for adjusting the engagement speed of a centrifugal clutch. During the operation of the centrifugal clutch, the clutch engages at a given rotational speed as determined by several factors one of which is the spring constant of the spring members. All things being equal, the engagement speed increases proportionally with the spring constant. Therefore, the engagement speed can be adjusted by replacing the existing spring members with spring members having different a spring constant. Under this method, the engagement speed is altered by changing the spring members as opposed to providing the clutch with adjustment holes in the weighted member, the drive, or both.
Various additional advantages, objects and features of the invention will become more readily apparent to those of ordinary skill in the art upon consideration of the following detailed description of the presently preferred embodiments taken in conjunction with the accompanying drawings.